Waking up with painful neck can be caused by one or more of the following:
- Sleeping position. When you sleep on your stomach, while you are sleeping your neck may be twisted to one side for hours at a time. This can strain your neck muscles, and make them feel sore and stiff in the morning.
- Pillow. Your head and neck spend many hours every night on your pillow, which is why choosing the right pillow is key to a healthy pain-free neck. A pillow that doesn’t support your head and neck properly can create tension in your neck muscles, and cause neck pain.
- Sudden movement. Sudden movements, like sitting up quickly can strain your neck muscles. Tossing and turning while you’re sleeping, or trying to sleep, can also create tension and stress in your neck.
- Previous injury. Some kinds of injuries, like sports injuries, may not always hurt at first. The full physical effects may only be felt days later. If you were injured in a way that might have hurt your neck, you may go to bed feeling okay, but wake up the next morning with a very sore, stiff neck.
- Other common causes of neck pain include: poor posture during the day, working too long at a computer, or watching television for too long without changing positions, osteoarthritis in one of the upper spinal joints, nerve compression caused by a herniated disk or bone spur in your neck. https://www.nhs.uk/conditions/neck-pain-and-stiff-neck/